How to address severe rust on plate bumper?

What is the best way to take care of this? Does por15 work?

 

Sand/sandblast it and then prime with self etching primer and then paint.

 

Yes POR 15 works as long as you follow the directions. Scrape off the loose rust and treat with POR15 metal prep per instructions. 2 coats of POR15 paint should seal it up nicely. If it's in the sun, you'll have to top coat it with another paint as POR15 is not UV stable. It'll last several years in the sun but will chalk up. I've used that stuff successfully on several cars/trucks. Three pointers:
1. Don't get it on your skin or you'll wear it for about 2 good weeks.
2. Don't open the can. Instead poke a small hole on the top side near the lid. Pour out what you need and then screw a sheet metal screw in the hole to seal the can.
3. Get cheap through away chip brushes and toss them after each use.